ARM: dts: stm32: add pwm cells to stm32f429

STM32 Timers support generic 3 cells PWM to encode PWM number, period and
polarity.

Fixes: c0e14fc7 ("ARM: dts: stm32: add Timers driver for stm32f429
MCU")
Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/boot/dts/stm32f429.dtsi

@@ -112,6 +112,7 @@ timers2: timers@40000000 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 
@@ -141,6 +142,7 @@ timers3: timers@40000400 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 
@@ -170,6 +172,7 @@ timers4: timers@40000800 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 
@@ -198,6 +201,7 @@ timers5: timers@40000c00 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 
@@ -267,6 +271,7 @@ timers12: timers@40001800 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 
@@ -288,6 +293,7 @@ timers13: timers@40001c00 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 		};
@@ -303,6 +309,7 @@ timers14: timers@40002000 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 		};
@@ -448,6 +455,7 @@ timers1: timers@40010000 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 
@@ -469,6 +477,7 @@ timers8: timers@40010400 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 
@@ -602,6 +611,7 @@ timers9: timers@40014000 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 
@@ -623,6 +633,7 @@ timers10: timers@40014400 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 		};
@@ -638,6 +649,7 @@ timers11: timers@40014800 {
 
 			pwm {
 				compatible = "st,stm32-pwm";
+				#pwm-cells = <3>;
 				status = "disabled";
 			};
 		};